Ethylene-vinyl alcohol copolymers (hereinafter, may be abbreviated as “EVOH(s)”) are polymeric materials that are superior in gas barrier properties against gases such as oxygen, oil resistance, antistatic properties, and the like. Thus, EVOH-containing resin compositions are molded into containers, films, sheets and the like, which have been widely used as blow-molded containers such as fuel containers and bottle containers as well as packaging materials, etc. In particular, as the blow-molded containers, multilayer structures have been widely employed which include: a layer formed of the EVOH-containing resin composition; a thermoplastic resin layer that is superior in moisture resistance, impact resistance, etc.; and the like.
In the production of the blow-molded containers, melt molding is generally conducted; however, the melt molding may result in impaired appearance of the molded articles through generation of defects such as gelation (dirt under paint) and streaks. In addition, the gelation and the like not only lead to impairment of the appearance of the molded articles, but also cause deterioration of performances; therefore, inhibition of these events is needed.
Furthermore, in the step of manufacturing blow-molded containers, an operation of the melt molding apparatus must be stopped once and restarted after a certain time period for a change of the resin, a halt in manufacture on weekends, etc., as well as a replacement operation of the molding die, and the like. In these instances, a small amount of the resin composition remaining in the melt molding apparatus may be deteriorated during the steps of elevation and lowering of the temperature of the apparatus, and gelled upon restarting, leading to the occurrence of a disadvantage of causing deterioration of appearance and qualities such as strength of the molded articles. Thus, after the restarting of the apparatus, it is necessary to conduct idling for a certain time period to await until such gels and the like is no longer generated and the appearance of the molded articles is reverted to the normal state. In light of the production cost, the time period required for the reverting is preferably short, in other words, a self-purge feature is preferably favorable; however it is impossible to conclude that the self-purge feature of conventional EVOH-containing resin compositions is favorable.
Therefore, as EVOH-containing resin compositions having an improved self-purge feature, (1) a resin composition prepared by adding a polyolefin resin, a carboxylic acid-modified polyolefin resin and an alkaline earth metal salt of a lower fatty acid having 9 or less carbon atoms to an EVOH resin at a specific ratio (see Japanese Unexamined Patent Application, Publication No. H5-255554), and (2) an EVOH-containing resin composition containing a carboxylic acid having a certain viscosity and a molecular weight of less than 75, and an alkaline earth metal salt at a specific ratio (see Japanese Unexamined Patent Application, Publication No. 2001-234008) have been known. However, due to containing the alkaline earth metal, these EVOH-containing resin compositions may cause coloring of the molded articles, and also the self-purge feature thereof is not satisfactory. In particular, the aforementioned EVOH-containing resin composition (1) is disadvantageous in that deterioration of the hue and impairment of the long-time operation properties, i.e., minimization of generation of the defects even in melt molding over a long time period (long-run workability), may occur, owing to the addition of the polyolefin resin. Additionally, an odor in molding must be taken into consideration from an environmental viewpoint.